You've got to break out the big guns when you perform for the queen, apparently. Earlier this month, 'X Factor' judge Nicole Scherzinger traded in her Pussycat Dolls costume for a phantom outfit -- 'Phantom of the Opera,' that is.

Scherzinger gave her best operatic performance in front of her Majesty Queen Elizabeth II at the annual Royal Variety Gala. She was chosen by composer Andrew Lloyd Webber to portray Christine among the four phantoms; the 'Phantom of the Opera' number was meant to commemorate the 25th birthday of the musical.

Also at the event, 'The Voice' judge Cee Lo Green delivered a rockin' rendition of his single 'Anyway,' and even performed a duet with Brit Leona Lewis on Queen's 'Somebody to Love,' which we're sure was much appreciated by the royal Queen herself.

Watch Nicole Scherzinger Sing Opera for the Queen

Watch Cee Lo Green and Leona Lewis Duet to 'Somebody to Love'